I dont think that's a fair assessment. There are two separate issues which ate being blurred.
The first issue, which the writer is complaining about, is people assuming his daughter is a boy based on her fashion choices.
The second issue, which apoears to be the concern of the people challenging the daughter in the article, is the issue of males of any age identifying as women and invading women's spaces and sports.
Because males are invading female spaces, women (or in the case of the article, the father of another girl) are exercising their right to challenge people they might suspect of wrongly occupying female spaces.
With adults, it's almost always possible to identify someone's sex, regardless of hair or dress. Only very occasionally do people get this wrong, and in those cases it's almost always mistaking a woman for a small man; very rarely do people mistake a man for a woman.
The problem is that in pre-teen children the secondary sex characteristics have not developed yet, so the only way to guess the sex of a child is by their hair and clothing.
For this reason, if I dress my 2 year old boy in a pink flowery top and put a bow in his hair, I can reasonably expect that strangers will assume he's a girl, and it would be downright stupid of me to get annoyed by this . If the same boy wears a skirt and crop top when he's 15, no one will assume he's a girl. The writer's 12 year old child is in between these two extremes, but is still pre-pubescent, therefore hair and clothing are the primary indicators of sex.
The writer of the article seems to misunderstand the position of those who are challenging his daughter. Her challengers are not saying "I don't think girls should be allowed to have short hair". They are saying "I don't think boys should be allowed in girls toilets"(correct) and "I think this child is a boy, based on the evidence available to me"(incorrect).
Perhaps if there weren't so many males trying to sneak into female spaces, then other parents wouldn't feel the need to be so vigilant, and would assume the short-haired child in the girls toilet was a girl, like they used to in the good old days.